This invention relates to vacuum drums of the kind used for gripping and feeding webs of various types, particularly webs of photographic material. More particularly, the invention relates to improvements in an unported, grooved vacuum drum.
An unported vacuum drum for gripping and feeding photographic webs is known from U.S. Pat No. 3,630,424, patented Dec. 28, 1971 in the name of John A. Rau and entlited Drilled Non-Ported Vacuum Drum. The Rau patent describes two kinds of commonly used vacuum drums. One kind has drilled holes of about 0.125 to 0.1875 inches in diameter through its shell and vacuum is applied to the holes from the drum exterior as the drum rotates. The holes are relatively large so that a porting or rotary valving system is used to disconnect the vacuum system from the portion or the drum not covered by the web. The other kind of commonly used vacuum drum discussed in the Rau patent is made from porous material and uses no porting. Air is pulled through the pores of the material even in those areas not covered by the web.
The improved vacuum drums disclosed in the Rau patent are of the non-ported kind. The Rau drums comprise a system of closely spaced small grooves in the outer surface of the drum, and vacuum feed slots that connect the grooves. A pattern of holes through the drum shell communicate with the grooves through the feed slots in the outer surface of the shell. When vacuum is supplied to the interior of the drum, air will flow along the grooves and feed slots through the holes into the interior of the drum for gripping a web in contact with the drum surface. Because the holes in the unported vacuum drum of Rau are small, e.g., less than 0.060 inches in diameter, they do not require porting as with the order commonly used of vacuum drums where the drilled holes were on the order of 0.125 to 0.1875 inches in diameter.
It is also known to shrink fit a sleeve over a roller. For example, U.S. Pat. No. 4,641,411 issued Feb. 10, 1987 to Stork Screens BV discloses a thick-walled roller covered with a non-perforated chromium sleeve. A perforated stencil or sieve is pushed over the sleeve on the roller. This is acomplished by first closing the perforations of the sieve by, for example, applying a removable fluid impervious layer around the sieve. With the cylinder and sieve in a vertical orientation the sieve is pushed upon as beveled portion of the roller. Then fluid under pressure is introduced into a space in the center of the roller and related passageways to cause the closed sieve to expanded and enable it to be pushed over the roller. The pressurized fluid acts as a lubricant during this movement. After the sieve is in place, the pressurized fluid is relieved and the sieve shrinks upon the roller.
Unported vacuum drums as generally described in the Rau patent have been in commercial use for a number of years. However, in some applications such drums are not entirely satisfactory. For example, when the drums are used in manufacturing areas where the web being driven is at a high temperature, i.e., near the glass transition temperature of the web, the grooves and slots in the outer surface of such vacuum drums may produce subtle lines in the web which adversely affect the overall finished pproduct quality. Also, some web coating enviroments use pinch roller drives. Such drives can generate polar charge patterns which survive web treatment operations in sensitizing and finally adversely influence the subsequent coating operations.